1. Field of the Invention
The present invention relates to the field of manufacture of nonwoven materials and resulting products. Because of the economy of manufacture and the wide variety of constructions and compositions, the growth of nonwovens as base materials has been quite rapid. Such materials may be produced at high speeds utilizing synthetic thermoplastic fibers with or without additional components or treatments depending upon the desired end use. In heavy basis weights where softness is not as critical such materials have found a wide range of applications from roadbed construction to home furnishings. In lighter basis weights, nonwovens have been particularly useful in the manufacture of disposable sanitary and infant care products as liners and absorbent materials. One use for which nonwovens in the middle basis weight range have found wide acceptance is for wiper products in the disposable and limited use areas. A selection is available of wiper materials that are particularly effective for clean wiping and absorbing both oily and aqueous liquids.
In most cases, however, the manufacture of nonwovens has involved a compromise between the economies of high speed manufacture and synthetic thermoplastics and the desirable soft, flexible tactile properties of conventional textiles. In some cases, it has also been necessary to sacrifice strength and other physical properties. As improvements to nonwoven manufacture are developed, the gap between these properties of conventional textile materials has narrowed. The present invention is directed to further improvements in nonwovens and their manufacture that achieve to a high degree bulk and other desirable textile-like properties while retaining the benefits of nonwovens. In particular, the present invention relates to the bonding of nonwoven materials and resulting products that achieve these and other desired results.
2. Description of the Prior Art
Much attention has been given the bonding of nonwoven fabrics. In general, bonding may be achieved by a variety of means. For example, such webs may be bonded autogenously by contacting the filaments or fibers in a tacky state. Alternatively, treatment with tackifying agents such as solvents or adhesives may be used. In many cases it is desirable to bond only within a patterned area to achieve a more flexible, fabric-like feel. Such pattern bonding may be obtained, for example, by patterned adhesive application or the application of heat and/or pressure in patterned areas. Representative of the latter type of bonding is U.S. Pat. No. 4,170,680 to Cumbers issued Oct. 9, 1979. This patent achieves a pattern of irregular bonds of continuous lands on one side and isolated projections on the other. A similar description is found in U.S. Pat. No. 4,005,169 to Cumbers dated Jan. 25, 1977. An earlier disclosure in U.S. Pat. No. 3,507,943 to Such, et al. dated Apr. 21, 1970 relates to a regular bond pattern obtained by opposing patterned rolls which contact at uniformly spaced apart areas. U.S. Pat. No. 3,636,147 to Rowland issued Jan. 18, 1972 relates to a process of bonding nonwovens in a pattern wherein the speed of one of the bonding rolls is varied to produce aesthetic visual bond appearances. U.S. Pat. No. 4,211,743 to Nauta, et al. dated Jul. 8, 1980 relates to opposing embossing patterns wherein one pattern is much finer than the other and resilient embossing surfaces are used for improving full contact with the bond pattern.
While these disclosures evidence progress to a more textile-like nonwoven material, results have not been completely satisfactory. Additional improvements in softness and in the ability to use shorter fibers while retaining bulk and strength are desired. In addition, further improvements in the properties of nonwovens for selected applications such as wipers are desired.